Refugee advocate Brami Jegan was one of 200 people gathered outside the detention centre and said a two-to-three storey building was well alight.

"I can see quite a few fires," Ms Jegan said. "The whole place seems to have pockets of fire everywhere."

The problems began yesterday morning when two asylum seekers took to the roof of one building reportedly in protest to the department denying their applications.

Refugee Action Coalition's Ian Rintoul said a total of 13 asylum seekers were on the roof by yesterday evening and were there when others on the ground started the fires.

Mr Rintoul remains in contact with some of the detainees who described the situation as chaotic.

He said one of the detainees told him: "We are too tired. I have never seen Villawood like this. Everyone is protesting. Everything is burning now."

Social Justice Network spokesman Jamal Daoud is also in contact with detainees who said that Serco security officers at Villawood have been attacked.

"The detainees attacked SERCO security with fire extinguishers and (were) throwing objects on them," Mr Daoud said in an email. "The detainees told me that they are experiencing difficult breathing because of this.

"There is total chaos inside the detention (centre), with detainees from the rooftop throwing roof tiles on the ground."

Ms Jegan said the 13 rooftop protesters - eight Afghans, three Kurds, two Iranians - had been in detention for between 13 and 20 months and were desperate.

About 150 detainees were protesting on the ground, she said.

Some of the detainees had been taken to a visitors' centre for their safety, she said.